I have made a few, and screwed up a few too.
I finally got over trying to make mine 12 oz and decided I wanted good coverage.
With a footbox, make it as tall as you are or maybe even add a couple.
If a drawstring footbox then you should add length for that.
Make sure the footbox is big enough. I wear a size 12 and made mine about 13" in diameter. Socks booties etc, and I did not want to press out the insulation and I wanted not to be constricted. That said I think most are around 12" in diameter.
If you are a side sleeper then you need a wider quilt since your knees and butt will be hanging out the side. If you sleep like you are in a coffin then you can make it more narrow IMO.
For me I find that I like a hex shape. IE narrow top. straight sides then taper at the feet.
The golite ultra 20 is more of a coffin shape.
The widest width at your torso should be as wide as your girth around your arms. Seems like I read Tim Marshalls recommendation of that but not sure.
At any rate I am 6'-3, about 230 today.
Both of these work for me. One is the Golite ultra 20 long, that I measured when I owned it. The other one is my latest XP/M50 quilt size. That is the one I am sticking with. I like the extra width but it adds a bit of weight.
The latest weighs 14.5 oz with 2.5 apex and M50 with a zipper and one side of the apex inside covered with 5mm silk.
It is a modular quilt.
tammons, I like the look of your tq design. I'm planning on making one soon and your idea seems like it would work well for a side sleeper.
You might want to get some cheap super light fleece on sale somewhere and do a test run.
Its still useful and if you screw up you havent lost much.
First XP M90 quilt I built I was trying to make it too light and it ended up too small. I ended up cutting it apart and used bits and pieces along with some other insul and M90 laying around to make a hooded jacket. Took me forever though but it is super warm and weighs 15 oz without the hood.
When I was sizing for my TQ project, I took a fleece blanket, used it like a top quilt and had my wife pin around my shoulders and feet at the appropriate length. Then, I added a few inches to the with to have some wiggle room.
I made one this week. I laid down and put my toes against the wall and put a pencil at the top of my head to determine length. Then I designed it on paper to be 36 at the feet and 48" ay the top.
I went with two layers of Primaloft One...
1.1 oz coyote brown for the inside, very soft, and 1.9 downproof black for the top.
Cut it, set it brown, black, insulation. Pinned it and sewed 3 sides. Turned it inside out by pulling the brown around. Then sewed the foot with a channel for shock cord. All that should be left is to put snaps on the foot box.
I say should, because I'm going to reopen it and put in another layer of insulation. Cost so gar about 66$ and 4~5 hours.
I think 48" at the top is to wide.